The present invention relates to an apparatus for drying substrates, such as semiconductor substrates, glass plates for liquid crystal devices or the likes (hereinafter referred to as substrates), through high speed rotation. More particularly, the invention relates to an improvement of apparatus of the type wherein the substrates are placed in a rotary member, which is rotated at high speed while fresh air is introduced into the apparatus, so that water droplets adhering on the substrates are dispersed by centrifugal force generated by rotation of the rotary member and the substrates are dried.
With such apparatus, the air or gas used for drying the substrates flows in a circumferential direction of a drying chamber and out through an exhaust duct, and a part of the water droplets dispersed from the substrates are apt to adhere to a peripheral inside wall of the chamber together with fine particles of dust. Not all of the air flows circumferentially in the drying chamber, and a part of the air whirls upwardly in turbulent currents. Such turbulent currents cause water droplets dispersed from the substrates or adhering on the peripheral inside wall to rebound upon or sprinkle over the substrates. Accordingly, the substrates to be dried are apt to be contaminated or impaired by such fine water droplets and fine particles of dust involved in the turbulent currents.
In order to solve the above drawback, proposes use of the Japanese laid-open (unexamined) apparatus patent application No. 60-59740 as shown in FIG. 5 of the accompanying drawings.
According to this laid-open application, the apparatus comprises a casing 101 defining a drying chamber 102 therein, and a rotary member 108 disposed in the drying chamber 102 and carrying a pair of cassettes 111, 111' in which the substrates are stored. The casing 101 includes a lid 103 defining an intake opening 104 for introducing ambient air or an appropriate inert gas, e.g. nitrogen gas, (hereinafter referred to just as air) into the drying chamber. The casing 101 defines an exhaust port 106 in a lower part thereof to be connected with an exhaust duct 107 for discharging the air whirling in the drying chamber therethrough. The rotary member 108 includes a base element 113 having a vane wheel for promoting smooth downward flows of air. Number 115 denotes guide vanes for guiding the downward flows of air.
This apparatus may indeed be improved in comparison with prior conventional apparatus. However, recent semiconductor technology requires that the quality of the substrates on which integrated circuits or desired circuit patterns are formed be extremely high. In view of this requirement, conventional apparatus including that mentioned above cannot meet the requirement, and are still insufficient therefor.
Several causes can be considered. Fine particles of dust are inevitably produced between a drive shaft 110 for rotating the rotary member 108 and a bearing thereof 114, and the fine particles of dust cannot be prevented in the conventional apparatus. The fine particles of dust cannot be completely discharged therefrom, because of lack of sufficient flows of air around the bearing. The turbulent currents caused in the drying chamber include fine particles of dust which serves to contaminate and impair the substrates to be dried.